There is no point in considering what must be avoided and how to avoid it when there is absolute certainty it will not be avoided, that's just wishful thinking and a waste of time.

It can be reduced considerably even so.

Should we do nothing?

It will take the flooding of a few major world cities perhaps, but action will happen.

Dont worry, we are doing something, western nations can all slap themselves on the back today at reducing carbon emissions by having outsourced our manufacturing to Asia. Too bad Asia is on the same planet as us though, ahh well. As to real action happening, don’t worry, Earth has survived far worse and life is damned hard to kill, it still bounces back after 70% extinction events although it takes an extra 10 million years or so to do it. Earth will probably slap us all silly with global weather alterations to the point where western people value the food they eat as much as people in the third world.... but that will slow carbon output a notch or two and certainly reduce rampant obesity in the west.